The present invention relates generally to a negative insert for cutting machining having a top side, a clearance side perpendicular thereto and a cutting edge in a region interconnecting these sides and extending substantially in parallel with these sides. The invention is generally directed to all types of negative inserts for cutting machining, such as inserts for turning as well as such for milling operation.
“Top side” is here defined as the side of the insert adapted to face opposite to the direction of rotation of a work piece to be machined by the insert in the case of a turning insert and the side adapted to face in the direction of rotation of the insert in the case of a milling insert. The axis of rotation of such a work piece is mostly horizontal, but should it for any reason not be horizontal the top side may have any orientation depending upon the direction of the axis of rotation. However, in this disclosure “uppermost” and other similar position definitions will relate to this top side as being on top of the insert.
Inserts for cutting machining with all types of negative geometries and of all conceivable types of material are included in the present specification. Inserts in the form of turning inserts will hereinafter be mainly discussed for illuminating the invention and the problem to be solved thereby without for that sake in any way restrict the invention thereto. The turning inserts often have more than one corner to engage a rotating work piece while being fixed in a tool holder for machining the work piece by a turning operation. When the wear of the uppermost flank of the clearance side has reached a predetermined level the required accuracy of the machining may not be guaranteed any longer, and the insert will in such a case be indexed in the tool holder for using another corner thereof for further turning operation. When the flank wear of all corners provided with a the cutting edge for turning operation have reached a certain width in this way the lifetime of the insert is expired.
The change, i.e., disposal, of such turning inserts is of course involved with costs, so that it is an on-going desire to prolong the life time of such inserts, for example by improving the properties of the material thereof.
Furthermore, variations of reaction forces of a rotating work piece machined by such an insert will give rise to vibrations in the insert and work piece, which may produce annoying noise and also will have a negative influence upon the result of the turning operation, i.e., increase the roughness of the generated surface. Another effect of vibrations could be reduced tool life.
In known turning inserts the cutting edge may be formed by a right angle corner interconnecting the top side and the clearance side, but it is also known to arrange a surface separating the cutting edge from the top side and making an angle to the top side of for instance 30° for strengthening the cutting edge and reducing the speed of the wear of the upper flank of the clearance side. The transition between the surface and the clearance side is then rounded off for improving the wear resistance and suppressing breaking of the insert in that region. Such an insert is known through for example U.S. Pat. No. 6,655,881.
It is desirable to provide an insert for cutting machining of the type defined in the introduction being improved in at least some aspect with respect to such negative inserts discussed above.
According to an aspect of the invention, the insert is provided with a flat or rounded chamfer connecting the cutting edge to the clearance side on at least one lateral side of the insert in the region of a corner thereof, and the chamfer makes an angle of 1°-15° with the clearance side for enabling application of the chamfer substantially tangentially to a work piece to be machined for bearing of the insert in two dimensions against the work piece during cutting machining operation carried out by the insert.
It has been found that such a chamfer extending the machining region of the insert during cutting machining operation to a surface results in a number of advantages with respect to negative inserts for cutting machining already known.
Vibrations of such an insert during cutting machining operation are remarkably reduced, especially in the tangential direction with respect to a work piece, which will rotate in the case of a turning insert. This results in an improved machining result, less wear upon the insert and less production of noise during the operation. The speed of the wear of the uppermost flank of the clearance side of the insert will also be reduced, so that a high accuracy machining may be carried out by the insert over a longer time within the tolerance range. Accordingly, need of adjustments in order to keep the accuracy at the machined work piece is reduced and the life time of the insert is prolonged, so that such inserts are not to be replaced as often as inserts already known.
U.S. Pat. No. 5,006,020 discloses a cutter insert having two bevels interconnecting the top side and the clearance side, but these are only made for strengthening the cutting edge, and the cutting edge is formed at the border of one of these bevels to the clearance side, and this bevel makes an angle of approximately 60° to the clearance side. Thus, this document does not show any chamfer being similar to or having a similar function to the chamfer in the insert according to the present invention.
According to an aspect of the invention the insert is a turning insert. Experiments have shown that vibrations of such a turning insert during turning operation are reduced remarkably.
According to another aspect of the invention the insert is a milling insert.
According to an aspect of the invention the chamfer makes an angle of 1°-10° or 3°-8° with the clearance side. It has been found that these are particularly suitable ranges for the angle of the chamfer for obtaining the advantages described above of an insert according to the invention.
According to another aspect of the invention the extension of the chamfer from the cutting edge to the clearance side is 0.03 mm-0.30 mm, 0.03 mm-0.20 mm, 0.04 mm-0.15 mm or 0.04 mm-0.08 mm. It has been found that a chamfer with an extension within these ranges will when applied substantially tangentially to a work piece to be machined enable efficient machining of the work piece thereby while achieving the advantages of less vibrations and reduced flank wear.
According to another aspect of the invention the chamfer is rounded with a radius r>10 mm, such as 10 mm<r<100 mm, 10 mm<r<50 mm or 10 mm<r<30 mm. A rounded or convex chamfer with such a radius exceeding 10 mm will result in a surface contact of the chamfer with respect to a work piece machined by the insert similar to a flat chamfer. The choice of a flat or such a rounded chamfer with such a large radius may be dependent upon the material intended to be machined by the insert.
According to another aspect of the invention the chamfer extends from the corner over at least substantially half the distance to an adjacent corner of the insert. This means that a cutting depth being up to half the distance between two adjacent corners of the insert may be chosen for cutting machining, such as turning operations carried out by use of the insert. The chamfer may also be arranged around substantially the entire top side of the insert, so that all corners thereof may be used for the operations.
According to another aspect of the invention the chamfer connects the cutting edge to the clearance side on both lateral sides of the insert joined by a the corner of the insert. It is preferred to have a the chamfer on both sides of a the corner for fully benefit from the advantages of the presence of such a chamfer during especially turning operations carried out.
According to another aspect of the invention the insert has a the chamfer connecting the cutting edge to the clearance side in the region of more than one corner of the insert, so that cutting machining, such as turning operations may be carried out while using more than one the corner of the insert and obtaining the advantages of the presence of such a chamfer.
According to another aspect of the invention the insert is provided with a convex wiper edge at least at one corner thereof, the wiper being defined by at least one radius. It is known that such a wiper geometry will reduce the roughness of the surface of the work piece machined with respect to a standard insert geometry having a rounded corner with one radius, and the wiper geometry in connection with the chamfer will improve the properties of the insert according to the invention even more.
According to another aspect of the invention at least the portions thereof intended to be applied to a work piece to be machined are made of boron nitride (BN). Boron nitride has physical properties making it well suited as a material for especially turning inserts, and it has turned out that inserts of this material having a chamfer according to the above gives rise to an excellent behaviour when carrying out cutting machining, especially turning operations thereby. The boron nitride is then preferably cubic boron nitride (CBN), but poly crystalline boron nitride (PCBN) is also advantageous.
According to another aspect of the invention the insert has a surface separating the cutting edge from the top side and making an angle to the top side of less than 40°.
Further advantages and advantageous features of the invention appear from the following description.